usb: gadget: Add kerneldoc for some neglected structure fields

A couple of structures in <linux/usb/gadget.h> have incomplete kerneldoc
comments, leading to these warnings in the docs build:

./include/linux/usb/gadget.h:230: warning: No description found for parameter 'claimed'
./include/linux/usb/gadget.h:230: warning: No description found for parameter 'enabled'
./include/linux/usb/gadget.h:412: warning: No description found for parameter 'quirk_altset_not_supp'
./include/linux/usb/gadget.h:412: warning: No description found for parameter 'quirk_stall_not_supp'
./include/linux/usb/gadget.h:412: warning: No description found for parameter 'quirk_zlp_not_supp'

Document those fields to make the warnings go away.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

include/linux/usb/gadget.h

@@ -188,6 +188,8 @@ struct usb_ep_caps {
  * @ops: Function pointers used to access hardware-specific operations.
  * @ep_list:the gadget's ep_list holds all of its endpoints
  * @caps:The structure describing types and directions supported by endoint.
+ * @enabled: The current endpoint enabled/disabled state.
+ * @claimed: True if this endpoint is claimed by a function.
  * @maxpacket:The maximum packet size used on this endpoint.  The initial
  *	value can sometimes be reduced (hardware allowing), according to
  *	the endpoint descriptor used to configure the endpoint.
@@ -349,6 +351,9 @@ struct usb_gadget_ops {
  *	or B-Peripheral wants to take host role.
  * @quirk_ep_out_aligned_size: epout requires buffer size to be aligned to
  *	MaxPacketSize.
+ * @quirk_altset_not_supp: UDC controller doesn't support alt settings.
+ * @quirk_stall_not_supp: UDC controller doesn't support stalling.
+ * @quirk_zlp_not_supp: UDC controller doesn't support ZLP.
  * @quirk_avoids_skb_reserve: udc/platform wants to avoid skb_reserve() in
  *	u_ether.c to improve performance.
  * @is_selfpowered: if the gadget is self-powered.